According to the Infonetics and Synergy Research Group, approximately 150,000 VoWLAN phones were sold in 2004. The research group predicts that in 2009, around 17 million VoWLAN phones will be sold and up to 100 million dual-mode handsets will be sold. In 2010, around 1 billion cell phones will be shipped. This means that even five years later, VoWLAN phones will still not have a major share of the mobile phone market.
Healthcare, retail, warehousing, and hospitality are four industries that have adopted VoWLAN. The standards-based wireless communicator from Vocera has enabled health-care workers to increase productivity, mobility, and accessibility. A VoWLAN solution, such as the one offered by SpectraLink, facilitates real-time inventory management by enabling communication between the truck-loaders and the warehouse staff. VoWLANs also improve customer care as a mobile staff can offer on-the-spot assistance. Hotels are using their Wi-Fi networks to allow guests to access the Internet and also to communicate with the housekeeping.
Improved QoS, greater deployment of Wi-Fi networks, and inexpensive handsets will further the acceptance of VoWLAN. Another obstacle to pervasive wireless deployments is the difficulty in transporting voice through wireless networks. By using an existing wireless LAN, a VoWLAN helps to improve the in-building coverage even in the sub-basement area. It helps to improve the cellular reception and does not require the installation of cellular repeaters. Even though dual-mode VoWLAN services can yield savings in mobile carrier charges, deploying a VoWLAN can be expensive.
A Wi-Fi handset costs upward of $ 400 and the existing wireless network in a company may require additional work before it can be deployed for VoWLANs. Frequently, the existing wireless network has to be replaced as a VoWLAN network requires dense and seamless RF coverage to enable access in places such as lifts, staircases, closets, restrooms, etc. VoWLANs allow users to access a single voicemail regardless of location and also to avail features such as four-digit dialing.
It is better to have an overlapping network while using VoWLANs in order to maintain the voice quality while roaming between access points. This is because the power output of a VoWLAN is not very high; it is between 20-50 milliwatts. It is not easy to maintain voice quality while roaming in VoWLAN deployments. In a cellular network, it is the cellular base stations that control the roaming behavior of a handset. This allows successful handoffs in the GSM and CDMA networks. In 802.11 wireless networks, the success rate of handoffs is not very high because the roaming is controlled by the handset.
Handsets that have not been optimized to work in a wireless network can lead to interruptions in the communication due to the roaming times. The 802.11k standard will allow handsets to access an AP table for looking up information regarding usage load, signal strength, and service set ID (SSID). The 802.11 standard impacts the number of calls supported by an AP. The 802.11b standard has a link rate of 11 Mbps and a throughput rate of around 6 Mbps; this allows it to support up to seven calls concurrently.
In order to overcome the capacity constraints, it is important to realize that different bands have different properties. Also, reducing the cell size is an option. However, this may result in a complex network design with increased overlaps and a possibility of increased co-channel interference. SpectraLink gateways provide a call-control mechanism for managing the number of calls on an AP. Meru Networks provides a similar mechanism called the voice services module (VSM) in its wireless infrastructural equipment. The VSM is an optional device.
The SpectraLink Voice Priority (SVP) is a proprietary standard that prioritizes voice packets over data packets. In the absence of appropriate QoS standards for wireless networks, packet loss, jitter, etc can affect voice quality even if the network is not heavily loaded. The 802.11e standard deals with QoS for wireless networks. Wi-Fi Multimedia (WMM) is a component of 802.11e and enables multilevel priority support, admission control, and auto power-save delivery. Multilevel priority support helps to prioritize traffic, Admission control enables the APs to accept or reject calls depending upon their capacity status. Automatic power-save enables a sleep function that allows handsets to wake up in time to receive the voice packets instead of being on power all the time.
As wireless handsets do not have a high processing power and they do not support the commonly used operating systems, they cannot be provided with internal Layer 3 security, which is possible with the existing VPN infrastructure.
VoWLAN location-discovery solutions as provided by companies such as Ekahau are not on par with the location-based telemetry or GPS solutions used by cellular networks to provide E911 services. The AP being used by the wireless handset can be made known to the public safety answering point (PSAP) by using ANI/ALI. High battery life is one of the main requisites for converged devices. Handsets are available with three days of standby and three hours of talk-time. Chipsets developed by companies such as Atheros and Texas Instruments have resulted in handsets that can function for longer periods between charges.